Trisoxalato complexes

K3[V(malonate)3] may be prepared by a procedure similar to that of the trisoxalato complex.272 The kinetics of ligand exchange have been studied by NMR line broadening 277 = 50 s 1 at 70 °C. 

There are numerous complexes of Cr(III) their stability is related to the (t2g) configuration. The chelate effect confers extra stability on the oxalato-(ethanedioato-) complexes. When water in the hexaaqua ion is replaced by three oxalate ligands, a trisoxalato-complex is formed in solution and can be readily prepared as a solid potassium salt. This exhibits optical isomerism. Geometrical isomerism is encountered in the cis- and tram- bisoxalato-complexes. The former exhibits optical isomerism. Although no solid containing the monooxalato-cation has been obtained, there is spectral evidence of its formation in solution. 

The solid can be prepared from the same reagents as the trisoxalato-complex but under different conditions, it can be also analysed for oxalate and water of crystallisation as above and for Cr by oxidation to Cr(Vl) using bromate. 

Unlike the previous complex, the trisoxalato-complex is moisture- and light-sensitive. Hence the necessity to adhere strictly to the instructions for the preparation, which involves the oxidation of the manganese (11) formed in the initial step (reduction of permanganate by oxalic acid). The second step ie the oxidation of Mn(II) by permanganate has to be done at below 0°C to avoid the thermal decomposition of the complex formed. Analysis is similar to the earlier complex. 

Iron(III) forms a trisoxalato-complex which can be precipitated as the potassium salt, by mixing FeCIs solution with K2C2O4 solution ... 

Prepare a KBr disc of your preparation and of the trisoxalato-complex prepared earlier and run the infrared spectra. Compare the spectra of the two preparations. 

Complexes of the hexammine cobalt(III) with trisoxalato-complexes... 

It is known that large anions tend to precipitate large cations whereas small anions form insoluble salts with small cations. Trisoxalato-complexes of the metals from Ti to Co are... 

Run the infrared spectra of the prepared complexes and compare them with the spectra of the trisoxalato-complexes used. Prepare KBr discs for running the spectra and assign the bands. 

Typical chelate complexes are trisoxalato ions, for example, [Co ox3]3-. Many mono-, di-, and trithio oxalates are also known.125... 

The reactions of both trisoxalato ferrate(III) and trisoxalatocobaltate-(III) with ascorbic acid have been examined. Evidence is presented in the reaction with Fe(III) for the formation of an intermediate prior to a relatively slow inner-sphere electron transfer reaction, which is independent of pH, ascorbic acid concentration, and ionic strength. For the cobalt complex, the pH (8-10) of the reaction medium leads to reaction with the doubly deprotonated ascorbate ion for which the rate constant is 20 s at 25 °C. Complexation of Fe(III) by... 

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